Method for controlling ph during planarization and cleaning of microelectronic substrates

ABSTRACT

A method and apparatus for processing a microelectronic substrate. In one embodiment, the method can include planarizing the microelectronic substrate with a planarizing liquid and rinsing the substrate with a rinsing liquid having a pH approximately the same as a pH of the planarizing liquid. The rinsing step can be completed while the substrate remains on a polishing pad of the apparatus, or, alternatively, the substrate can be removed to a rinsing chamber for rinsing. In another embodiment, the method can include conditioning the polishing pad by removing polishing pad material from the polishing pad and then cleaning the microelectronic substrate by engaging the substrate with the same polishing pad and moving at least one of the polishing pad and the substrate relative to the other of the polishing pad and the substrate after conditioning the polishing pad.

TECHNICAL FIELD

The present invention relates to mechanical and chemical-mechanicalplanarization of microelectronic substrates. More particularly, thepresent invention relates to controlling the pH of a microelectronicsubstrate during planarization and post-planarization processing of themicroelectronic substrate.

BACKGROUND OF THE INVENTION

Mechanical and chemical-mechanical planarization processes removematerial from the surfaces of semiconductor wafers, field emissiondisplays, and many other microelectronic substrates to form a flatsurface at a desired elevation. FIG. 1 schematically illustrates aplanarizing machine 10 with a platen or base 20, a carrier assembly 30,a polishing pad 41 positioned on the platen 20, and a planarizing liquid44 on the polishing pad 41. The planarizing machine 10 can also have anunder-pad 25 attached to an upper surface 22 of the platen 20 forsupporting the polishing pad 41. In many planarizing machines, a driveassembly 26 rotates (arrow A) and/or reciprocates (arrow B) the platen20 to move the polishing pad 41 during planarization.

The carrier assembly 30 controls and protects a substrate 12 duringplanarization. The carrier assembly 30 generally has a substrate holder32 with a pad 34 that holds the substrate 12 via suction. A carrierdrive assembly 36 typically rotates and/or translates the substrateholder 32 (arrows C and D, respectively). Alternatively, the substrateholder 32 can include a weighted, free-floating disk (not shown) thatslides over the polishing pad 41.

The combination of the polishing pad 41 and the planarizing liquid 44generally defines a planarizing medium 40 that mechanically and/orchemically-mechanically removes material from the surface of thesubstrate 12. The polishing pad 41 may be a conventional polishing padcomposed of a polymeric material (e.g., polyurethane) without abrasiveparticles, or it may be an abrasive polishing pad with abrasiveparticles fixedly bonded to a suspension material. In a typicalapplication, the planarizing liquid 44 may be a chemical-mechanicalplanarization slurry with abrasive particles and chemicals for use witha conventional non-abrasive polishing pad. In other applications, theplanarizing liquid 44 may be a chemical solution without abrasiveparticles for use with an abrasive polishing pad. In any case, theplanarizing liquid 44 can be pumped from a planarizing liquid supply 45through a conduit 46, and through orifices 43 to a planarizing surface42 of the polishing pad 41.

To planarize the substrate 12 with the planarizing machine 10, thecarrier assembly 30 presses the substrate 12 against the planarizingsurface 42 of the polishing pad 41 in the presence of the planarizingliquid 44. The platen 20 and/or the substrate holder 32 then moverelative to one another to translate the substrate 12 across theplanarizing surface 42. As a result, the abrasive particles and/or thechemicals of the planarizing medium 40 remove material from the surfaceof the substrate 12.

After the substrate 12 has been planarized, particulate matter, such asabrasive particles, particles removed from the polishing pad 41, and/orparticles removed from the substrate 12 may adhere to the substrate.Accordingly, the substrate 12 can be rinsed to remove the particulatematter before the substrate 12 undergoes additional processing. Oneconventional approach to rinsing the substrate 12 is to pump a rinsingsolution 53 from a rinsing solution supply 54 through the orifices 43 tothe planarizing surface 42 of the polishing pad 41. The rinsing solution53 rinses the substrate 12 while the substrate remains in situ on thepolishing pad 41. The rinsing solution 53 may be introduced to thepolishing pad 41 as the relative velocity between the substrate 12 andthe polishing pad 41 is reduced or ramped down.

Another rinsing approach, which can be used in addition to or in lieu ofthe in situ approach discussed above, can include removing the substrate12 from the polishing pad 41 with a substrate transporter 60 and movingthe substrate 12 to a rinse chamber 50. The substrate transporter 60 caninclude a grasping device 62 that engages the substrate 12 after thesubstrate has been detached from the carrier assembly 30. The substratetransporter 60 can further include one or more movable arms 61 that canrobotically move the substrate 12 to the rinse chamber 50. The rinsechamber 50 can include a plurality of opposing spray bars 51, eachhaving a plurality of nozzles 52 for directing a spray of the rinsingsolution 53 onto the substrate 12. The rinse chamber 50 shown in FIG. 1can simultaneously accommodate two substrates 12 positioned upright inadjacent bays 57.

A third approach to removing particulate matter from the substrate 12 isto remove the substrate from the polishing pad 41 and place thesubstrate 12 on a separate buffing pad (not shown). The buffing pad thenmoves relative to the substrate and may also be supplied with a rinsingsolution to convey the particulate matter away.

After the substrate 12 has been planarized and rinsed, the polishing pad41 can be conditioned to restore its ability to planarize additionalsubstrates. Accordingly, the planarizing machine 10 can include aconditioner 70 that removes polishing pad material from the planarizingsurface 42 to expose new polishing pad material. The conditioner 70 caninclude an abrasive disk 71 for mechanically roughening the planarizingsurface 42 of the polishing pad 41. The conditioner 70 can also includea conditioning fluid source 72 that supplies conditioning fluid to thepolishing pad 41 for chemically conditioning the planarizing surface 42of the polishing pad 41.

Planarizing processes must consistently and accurately produce auniformly planar surface on the microelectronic substrate 12 to enableprecise fabrication of circuits and photo-patterns. As the density ofintegrated circuits 30 increases, the uniformity and planarity of thesubstrate surface is becoming increasingly important because it isdifficult to form sub-micron features or photopatterns to within atolerance of approximately 0.1 microns on non-uniform substratesurfaces. Thus, planarizing processes must create a highly uniform,planar surface on the substrate.

One drawback with the conventional methods discussed above is that theymay not create a sufficiently planer surface on the substrate becauseparticulates may remain attached to the substrate as a result of contactbetween the substrate 12 and a variety of chemical solutions during andafter planarization. For example, in one conventional method theplanarizing solution is an ammonia-based solution, and the rinsing andconditioning fluids are deionized water. Each chemical solution may havedifferent chemical characteristics and sequentially exposing themicroelectronic substrate 12 to different chemical solutions may causeparticulates to adhere to the surfaces of the substrate. Theseparticulates may damage the wafer during subsequent polishing andhandling steps, or may interfere with subsequent processing steps, suchas masking and etching. Furthermore, the particulates may becomeincorporated into the devices formed on the substrate, potentiallycausing the devices to fail.

In the competitive semiconductor and microelectronic devicemanufacturing industries, it is desirable to maximize the throughput offinished substrates. Accordingly, a further drawback with theconventional processes described above is that they may requireadditional time to remove the particulates from the substrate. Theadditional time can be required because the substrate has additionalparticulate adhered to it as a result of exposure to various chemicalsolutions.

SUMMARY OF THE INVENTION

The present invention is directed toward methods and apparatuses forprocessing a microelectronic substrate. In one embodiment, the apparatuscan include a polishing pad having a planarizing surface and a source ofplanarizing liquid in fluid communication with the planarizing surfaceof the polishing pad. The microelectronic substrate is planarized byengaging the substrate with the polishing pad while the planarizingliquid is disposed on the polishing pad, and moving one of the substrateand the polishing pad relative to the other of the substrate and thepolishing pad. As the relative motion between the substrate and thepolishing pad is decreased, rinsing fluid having a pH approximately thesame as a pH of the planarizing liquid can be introduced to theplanarizing surface to maintain the pH of the microelectronic substrateat an approximately constant level.

In another embodiment, the microelectronic substrate can be removed fromthe polishing pad and rinsed remotely with a rinsing liquid having a pHapproximately the same as a pH of the planarizing liquid. The rinsingliquid in either of the foregoing embodiments can be selected to includetetramethyl ammonium hydroxide and deionized water, or other substanceswhere a pH of the rinsing liquid is approximately the same as the pH ofthe planarizing liquid.

In still another embodiment, the polishing pad can include anon-abrasive polishing pad and the planarizing liquid can include anabrasive slurry. The pH of the microelectronic substrate can bemaintained by maintaining the pH of the abrasive slurry at anapproximately constant level as the relative velocity between themicroelectronic substrate and the polishing pad is reduced toapproximately zero.

In yet another embodiment of the invention, the polishing pad can beconditioned by supplying to the polishing pad a conditioning liquidhaving a pH approximately the same as the pH of the planarizing liquid.In still a further embodiment, the microelectronic substrate can becleaned by engaging the microelectronic substrate with the polishingpad, after the polishing pad has been conditioned, and moving at leastone of the polishing pad and the substrate relative to the other of thepolishing pad and the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation view of a planarizing machine inaccordance with the prior art.

FIG. 2 is a schematic side elevation view of a planarizing machinehaving a source of rinsing liquid and a source of planarizing liquid,each liquid having an approximately equal pH in accordance with anembodiment of the present invention.

FIG. 3 is a schematic side elevation view of a planarizing machinehaving a source of conditioning liquid and a source of planarizingliquid, each liquid having an approximately equal pH in accordance withanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an apparatus and method for mechanical and/orchemical-mechanical planarization of substrates used in the manufactureof microelectronic devices. Many specific details of certain embodimentsof the present invention are set forth in the following description andin FIGS. 2-3 to provide a thorough understanding of such embodiments.One skilled in the art, however, will understand that the presentinvention may have additional embodiments or that the invention may bepracticed without several of the details described in the followingdescription.

FIG. 2 is a schematic side elevation view of a CMP machine 110 having aplaten 120 and a planarizing medium 140. In one embodiment, the CMPmachine can include a model number 676 manufactured by IPEC Corp. ofPortland, Oreg., and in other embodiments, the CMP machine can includeother devices, such as a web-format planarizing machine, manufactured byEDC Corporation. In the embodiment shown in FIG. 2, the planarizingmedium 140 includes a polishing pad 141 and an under-pad 125 releasablyattached to the platen 120. The planarizing medium can further include aplanarizing liquid 144 disposed on a planarizing surface 142 of thepolishing pad 141. The platen 120 can be movable by means of a platendrive assembly 126 that can impart a rotational motion (indicated byarrow A) and/or a translational motion (indicated by arrow B) to theplaten 120. As was discussed above, the CMP apparatus 110 can alsoinclude a carrier assembly 130 having a substrate holder 132 and aresilient pad 134 that together press a microelectronic substrate 112against the planarizing surface 142 of the polishing pad 141. A carrierdrive assembly 136 can be coupled to the carrier assembly 130 to movethe carrier assembly axially (indicated by arrow C) and/or rotationally(indicated by arrow D) relative to the platen 120.

The planarizing liquid 144 can be supplied to the polishing pad 141 froma planarizing liquid supply 145 via a conduit 146. In one embodiment,the conduit 146 can include a flexible coupling 147, shown schematicallyin FIG. 2, to allow for translational or rotational motion of the platen120 relative to the planarizing liquid supply 145. The coupling 147 canbe connected to a manifold 148 in the platen 120. The manifold 148 caninclude a plurality of orifices 143 that extend upwardly through theunder-pad 145 and the polishing pad 141 to the planarizing surface 142of the polishing pad. As the carrier assembly 130 moves relatively tothe platen 120, the planarizing medium 140 (i.e., the polishing pad 141and/or the planarizing liquid 144) removes material from themicroelectronic substrate 112. The process may also cause material to beremoved from the polishing pad 141.

Particulates removed from the microelectronic substrate 112 and thepolishing pad 141, as well as abrasive elements in the planarizingliquid 144 may tend to adhere to the microelectronic substrate 112.Accordingly, the CMP machine 110 can include a rinsing liquid 153 thatis pumped from a rinsing liquid supply 154 through the conduit 146 tothe orifices 143 in the polishing pad 141. The conduit 146 can include avalve 149 that can be adjusted to couple the rinsing liquid supply 154and/or the planarizing liquid supply 145 with the orifices 143, toselectively provide rinsing liquid 153 and/or planarizing fluid 144 tothe polishing pad 141.

It has been observed that particulates adjacent to the substrate 112 mayhave a greater tendency to adhere to the substrate 112 when the pH ofthe substrate changes suddenly. Accordingly, in one embodiment of theinvention, the rinsing liquid 153 is selected to have a pH approximatelythe same as a pH of the planarizing liquid 144, to maintain the pH ofthe substrate 112 at an approximately constant level as the substrate112 is exposed to the rinsing liquid 153. In one embodiment, the CMPmachine 110 can include a pH meter 158 coupled to the rinsing liquidsupply 154 and the planarizing liquid supply 145 to monitor the pHlevels of both liquids. The pH meter can include a conductivity meter orother device that detects pH.

In one embodiment, the planarizing liquid 144 can include Klebosol, anammonia-based solution available from Rodel Corp. of Newark, Del. havinga pH in the range of approximately 10.6 to approximately 11.4, and moreparticularly, approximately 11.0. The pH of the rinsing liquid 153 canbe selected to have a pH in approximately the same range. In oneembodiment, the rinsing liquid 153 can include a mixture of deionizedwater provided by a deionized water supply 155 and tetramethyl ammoniumhydroxide (TMAH) provided by a TMAH supply 156. The relative amount ofdeionized water and TMAH included in the rinsing liquid 153 can becontrolled by adjusting a rinsing liquid valve 157 coupled between thedeionized water supply 155 and the TMAH supply 156. In one embodiment,the rinsing liquid 153 can include 99.994% deionized water and 0.006%TMAH by volume, to have a pH of approximately 11.0. In otherembodiments, the planarizing liquid 144 and the rinsing liquid 153 caninclude other compositions having other pHs, so long as the pH of therinsing liquid 153 is selected to be approximately the same as the pH ofthe planarizing liquid 144.

In another aspect of this embodiment, the rinsing liquid 153 can beselected to have an electrical charge that is approximately the same asan electric charge of the planarizing liquid 144. For example, in oneembodiment, the electrical charge of the rinsing liquid 153 and theplanarizing liquid 144 can be selected to be approximately zero toreduce the likelihood of imparting unwanted electrical charges to thesubstrate 112. In other embodiments, the substrate 112, the rinsingliquid 153, and/or the planarizing liquid 144 can have other non-zeroelectrical charges.

The CMP machine 110 can also include a substrate transporter 160 and arinse chamber 150. As was discussed above, the substrate transporter 160can include a plurality of articulated movable arms 161 coupled to agrasping device 162. The grasping device 162 can engage the substrate112 after it has been released from the carrier assembly 130 and thearms 161 can be controlled to robotically transfer the substrate 112 tothe rinse chamber 150. The rinse chamber 150 can include spray bars 151positioned on opposite sides of adjacent rinse bays 157. The spray bars151 can direct the rinsing liquid 153 through nozzles 152 toward thesubstrate 112 to clean opposing surfaces of the substrate 112 when thesubstrate is positioned in one of the rinse bays 157.

The rinsing liquid 153 can have a pH that is approximately the same asthe pH of the planarizing liquid 144, to maintain the pH of thesubstrate 112 at an approximately constant level for an additionalportion of the post-planarization processing operation. In one aspect ofthis embodiment, the rinsing fluid 153 can be supplied from the samerinsing liquid supply 154 that supplies rinsing liquid the polishing pad141. Accordingly, the valve 149 can be adjustable to provide the rinsingsolution 153 to the polishing pad 141 and/or the rinsing chamber 153, aswell as provide the planarizing liquid 144 to the polishing pad 141.

In operation, the planarizing liquid 144 is pumped from the planarizingliquid supply 145 through the orifices 143. The microelectronicsubstrate 112 engages the planarizing surface 142 of the polishing pad141 while the platen 120 and/or the carrier assembly 130 are movedrelative to each other to planarize the microelectronic substrate 112.As the planarizing process nears completion, the relative velocitybetween the microelectronic substrate 112 and the polishing pad 141 isramped down or reduced to zero by gradually halting the motion of theplaten 120 and/or the carrier assembly 130.

As the relative velocity between the substrate 112 and the platen 120decreases, the flow of planarizing liquid 144 is halted and the rinsingliquid 153 is supplied to the polishing pad 141. In one embodiment, thetime required to halt the relative motion between the substrate 112 andthe polishing pad 141 (and accordingly, the time during which thesubstrate 112 is rinsed on the polishing pad 141), is in the range ofapproximately twenty to approximately forty seconds, and preferablyapproximately forty seconds. In other embodiments, the substrate 112 canbe rinsed on the polishing pad 141 for greater or lesser periods oftime, depending upon, for example, the initial relative velocity betweenthe substrate 112 and the polishing pad 141, the normal force betweenthe substrate 112 and the polishing pad 141, and the fluidcharacteristics of the planarizing liquid 144 and the rinsing liquid153.

Once the relative motion between the microelectronic substrate 112 andthe polishing pad 141 is halted, the carrier assembly 130 disengagesfrom the substrate 112 and the substrate transporter 160 engages thesubstrate 112 and removes the substrate from the polishing pad 141. Thesubstrate transporter 160 moves the substrate 112 to the rinse chamber150 where the substrate is sprayed with the rinsing solution 153. In oneembodiment, the substrate 112 can be rinsed for approximately fiveseconds in the rinse chamber, and in other embodiments, the substratemay be rinsed for greater or lesser periods of times.

An advantage of the CMP machine 110 and the process described above withreference to FIG. 2 is that the substrate 112 can be maintained at anapproximately constant pH level throughout the planarization, ramp down,and rinsing operations. This is advantageous because particulate matter,such as material removed from the substrate 112, material removed fromthe polishing pad 141, and/or abrasive particles in the planarizingliquid 144 may be less likely to adhere to the microelectronic substrate112 when the pH of the substrate 112 remains approximately constant.Accordingly, the likelihood of contaminating the substrate 112 withparticulate matter can be substantially reduced, increasing the numberof defect-free substrates. The absence of particulate matter may also beadvantageous because post-CMP processing steps, such as masking, may bemore accurately performed without the interference created by theparticulate matter.

Another advantage of the CMP machine 110 and process described abovewith reference to FIG. 2 is that the machine can increase the throughputof substrates 112. For example, conventional CMP methods that includechanging the pH of the substrate 112 before all of the particulates havebeen removed may require that the substrate be rinsed in a rinse chamberfor approximately thirty seconds. By contrast, the process describedabove can include rinse times in the rinse chamber 150 on the order ofapproximately five seconds.

Still referring to FIG. 2, the CMP machine 110 can be operated inaccordance with another embodiment of the invention by supplying theplanarizing fluid 144 to the polishing pad 141 during both theplanarization and ramp-down steps. Accordingly, the pH of themicroelectronic substrate 112 can remain approximately constant duringboth the planarization and ramp-down steps. The substrate 112 can thenbe moved directly to the rinse chamber 150 and rinsed with the rinsingliquid 153 without first rinsing the substrate 112 on the polishing pad141. An advantage of this process is that it does not require therinsing solution supply 154 to be coupled to the polishing pad 141,potentially simplifying the CMP machine 110. Conversely, an advantage ofrinsing the substrate 112 on the polishing pad 141 before moving thesubstrate to the rinse chamber 150 is that the additional rinse step mayincrease the likelihood that any particulate matter adhering to thesubstrate 112 is removed.

FIG. 3 is a schematic side elevation view of a CMP machine 210 having aconduit 246 that delivers fluid downwardly onto the planarizing surface142 of the polishing pad 141, in accordance with another embodiment ofthe invention. Accordingly, an advantage of the CMP machine 210 whencompared with the CMP machine 110 shown in FIG. 2 is that the need fororifices 143 (FIG. 2) and a manifold 148 (FIG. 2) is eliminated,potentially simplifying the construction and maintenance of the CMPmachine 210. Conversely, an advantage of the CMP machine 110 is that itmay more uniformly distribute the planarizing fluid 144 over theplanarizing surface 142, and may distribute the planarizing fluid 144independent of the location of the carrier assembly 130.

As is also shown in FIG. 3, the CMP machine 210 can include aconditioner 270 to refurbish the polishing pad 141 after planarization.In one embodiment, the conditioner 270 can include an abrasive disk 271that roughens the planarizing surface 142 of the polishing pad 141 andremoves polishing pad material from the planarizing surface. Theconditioner 270 can also include a conditioning fluid source 272 inaddition to or in lieu of the abrasive disk 271, for removing polishingpad material from the polishing pad 141. In one embodiment, theconditioning fluid can be chemically active to chemically remove thepolishing material. In another embodiment, the conditioning fluid can bechemically inactive, but can act to flush the removed polishing padmaterial away from the polishing pad 141. In either case, a pH of theconditioning fluid can be selected to be approximately the same as thepH of the planarizing liquid 144. For example, the conditioning fluidcan have the same chemical composition as the rinsing liquid 153.Accordingly, the conditioning fluid can be supplied by the rinsingsolution supply 154 in one embodiment and the separate conditioningfluid source 172 can be eliminated.

In operation, the CMP machine 210 can be initially operated according tothe steps discussed above with reference to FIG. 2 to planarize thesubstrate 112. In one embodiment, the substrate 112 can be moveddirectly to the rinse chamber after planarization (as was generallydiscussed above with reference to FIG. 2). Alternatively, the polishingpad 141 can be conditioned after planarization, and the substrate 112can be buffed or cleaned on the conditioned polishing pad 141. Forexample, the polishing pad 141 can be conditioned by moving the abrasivedisk 271 over the planarizing surface 142 and/or by flushing theplanarizing surface 142 with the conditioning liquid. After theconditioning step has been completed, the substrate 112 can be buffed bymoving the substrate 112 relative to the newly conditioned planarizingsurface 142 in the presence of the rinsing solution 153. The buffingstep can remove substrate material from the substrate 112 and/or canremove particulates that adhere to the surface of the substrate 112. Inone embodiment, the ramp-down time can be reduced from a range of twentyto forty seconds to a range of approximately ten to approximately thirtyseconds (preferably approximately fifteen seconds) when the ramp-downstep is followed by the buffing step. Optionally, the substrate 112 canthen be rinsed in the rinse chamber 150.

One advantage of the CMP machine 210 and the process discussed abovewith reference to FIG. 3 is that the conditioning fluid has a pHapproximately the same as the pH of the planarizing liquid 144.Accordingly, the pH of the polishing pad 141 can be maintained at anapproximately constant level, increasing the likelihood that thesubstrates 112 contacting the polishing pad 141 also remain at anapproximately constant pH. As discussed above, keeping the pH of themicroelectronic substrate 112 at an approximately constant level canreduce the tendency for particulate matter to adhere to the substrate112.

Another advantage of the process described above with reference to FIG.3 is that the microelectronic substrate 112 can be buffed on the samepolishing pad 141 as was used to planarize the substrate 112, unlikesome conventional methods which require a separate buffing pad. This isadvantageous because it can reduce the number of pads necessary for CMPand post-CMP processing, and can also increase throughput by eliminatingthe step of moving the wafer from the polishing pad to a separatebuffing pad.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. An apparatus for processing a microelectronic substrate, comprising:a polishing pad having a planarizing surface; a source of planarizingliquid in fluid communication with the planarizing surface of thepolishing pad; and a source of rinsing liquid in fluid communicationwith the planarizing surface of the polishing pad, the source of rinsingliquid having a rinsing liquid with a chemical composition differentthan a chemical composition of the planarizing liquid and a pHapproximately the same as a pH of the planarizing liquid. 2-77.(canceled)